Generation and Trapping of Cyclopropenes from 2-Alkoxy-1,1-dichlorocyclopropanes

In presence of crown ether, 2-alkoxy-1,1-dichlorocyclopropanes react with t-BuOK/THF preferentially via ring opening to 2-chloroalk-2-en-1-ones and alkynones or to chlorocyclopropenes. The latter may be intercepted with 1,3-diphenylisobenzofuran, but in the absence of trapping agent, the rearrangement to vinylcarbenes does not occur.     

Cationic Gold(III) Alkyl Complexes: Generation,Trapping, and Insertion of Norbornene

Migratory insertion of alkenes into gold–carbon bonds, a fundamental yet unprecedented organometallic transformation, has been investigated from a discrete (P,C) cyclometalated gold(III) dimethyl complex. Methide abstraction by B(C₆F₅)₃ is shown to generate a highly reactive cationic Au^III complex that evolves spontaneously by C₆F₅ transfer from boron. In the presence of norbornene, migratory insertion into the Au C bond proceeds readily. The resulting norbornyl complex is efficiently trapped with pyridines or chloride to give stable four‐coordinate adducts.     

Cationic Gold(III) Alkyl Complexes: Generation,Trapping, and Insertion of Norbornene

Migratory insertion of alkenes into gold–carbon bonds, a fundamental yet unprecedented organometallic transformation, has been investigated from a discrete (P,C) cyclometalated gold(III) dimethyl complex. Methide abstraction by B(C₆F₅)₃ is shown to generate a highly reactive cationic Au^III complex that evolves spontaneously by C₆F₅ transfer from boron. In the presence of norbornene, migratory insertion into the Au? C bond proceeds readily. The resulting norbornyl complex is efficiently trapped with pyridines or chloride to give stable four‐coordinate adducts.     

Generation and Trapping of Acyl Nitrile Oxides from Substituted Aryl 1,3 Diketones in a Nitrating Mixture

Acyl nitrile oxides are readily generated and trapped in a nitrating mixture with N-methylmaleimide.     

Directed Gas‐Phase Synthesis of Triafulvene under Single‐Collision Conditions

The triafulvene molecule (c‐C₄H₄)—the simplest representative of the fulvene family—has been synthesized for the first time in the gas phase through the reaction of the methylidyne radical (CH) with methylacetylene (CH₃CCH) and allene (H₂CCCH₂) under single‐collision conditions. The experimental and computational data suggest triafulvene is formed by the barrierless cycloaddition of the methylidyne radical to the π‐electron density of either C₃H₄ isomer followed by unimolecular decomposition through elimination of atomic hydrogen from the CH₃ or CH₂ groups of the reactants. The dipole moment of triafulvene of 1.90 D suggests that this molecule could represent a critical tracer of microwave‐inactive allene in cold molecular clouds, thus defining constraints on the largely elusive hydrocarbon chemistry in low‐temperature interstellar environments, such as that of the Taurus Molecular Cloud 1 (TMC‐1).     

Photolytic Studies on the Generation and Trapping of 6-Oxomethylidenecyclohexa-2,4-diene-1-one Derivatives with Various Nucleophiles

α-Oxoketenes and cyclohexadiene α-oxoketenes are reactive intermediates, particularly the latter due to their high re-aromatization potential. In this communication, we report photolytic studies on the generation of such species from 4-OMe and 4-OMOM protected resorcylate dioxinones and their trapping to give resorcylate esters and amides as well as the formation of adducts with enol-ethers as trapping reagents.     

Determination of Germanium and Tin and Inorganic Tin Species by Hydride Generation in Situ Trapping Flame Atomic Absorption Spectrometry

The analytical performances of a coupled hydride generation, integrated atom trap (HG-IAT) atomizer flame atomic absorption spectrometry (FAAS) system were evaluated for determination of Ge and Sn and inorganic tin species in environmental samples. Germanium and tin hydrides were atomized in air-acetylene flame-heated IAT. A new design of HG-IAT-FAAS hyphenated technique that would exceed the operational capabilities of existing arrangements (a water-cooled single silica tube, double-slotted quartz tube) permitting construction of an “integrated trap” was investigated. For the estimation of Sn(II) and Sn(IV) concentrations in samples, the difference between the analytical sensitivities of the absorbance singnals obtained for tin hydride without and with previous treatment of samples with L-cysteine could be used. The concentration of Sn(IV) was calculated by the difference between total Sn(tot) and Sn(II). An improvement in limit of detection was achieved compared with that obtained using any of the aforementioned atom trapping techniques separately. The concentration limits of detection were 25 and 8 ng mL^?1 for Ge and Sn, respectively. For a 2 min in situ preconcentration time, sensitivity enhancement, compared to FAAS, were 10 and 14 folds for Ge and Sn, respectively, using hydride generation atom trapping technique. The sensitivity can be further improved by increasing the collection time. The relative standard deviations (RSDs) are of the order of 5–10% for this hyphenated technique. The designs studied include slotted tube, single silica tube, and integrated atom trap water-cooled atom traps. The accuracy of this method was tested by analyses of BCS-CRM No.346 (Alloy), GBW 07302 (Stream Sediment), PACS-1 (Marine Sediment), NBS SRM 1633a (Coal Fly Ash), and NIST SRM 1643e (Trace Element in Water) certified reference materials. Agreement between analytical results and certified values for the test elements Ge and Sn (in the range of 1.7–91.0 µg g^?1) were in agreement with recommended values. The measured Ge and Sn contents in five referenced materials were in satisfactory agreement with the certified values. The hyphenated technique was applied for germanium and tin determination in coal fly ash, soil, sediment, garlic, sewage, and river water.     

Generation and Trapping Reactions of a Formal 1:1 Complex between Singlet Carbon and 2,2′-Bipyridine

The structural element of a protonated imidazolium system was realized for the first time in the synthesis of 1 from 2,2′-bipyridine and a novel methylenating agent. Reversible deprotonations proceed via 2 to lead to carbene 3 , a formal 1:1 complex between singlet carbon and 2,2′-bipyridine which is stable in solution and can be trapped. For 1 and 2 , unusual hybridizations of the bridging C atom were found experimentally.     

Spatial Taming and Trapping of Molecules

Molecular beam techniques for study of collisional and spectroscopic processes have recently been enhanced by use of static electric or magnetic fields to orient or align molecules with permanent dipole moments. A more general method is now in prospect, applicable both to alignment and to spatial trapping of molecules. This exploits the anisotropic interaction of the electric field vector of intense laser radiation with the dipole moment induced in a polarizable molecule by the laser field. The interaction creates directional superpositions of field-free states that correspond to oblate spheroidal wavefunctions, with eigenenergies that decrease with increasing field strength. We suggest that this polarizability interaction produces the marked alignment found in laser-induced dissociative ionization of CO by the Saclay group. We also present calculations illustrating the feasibility of spattal trapping. In combination with supermirror focussing and buffer-gas cooling, an intense infrared laser can typically confine molecules for long-times (-hours) within a small (-picoliter) and cold (?1°K) “pocket of light.”     

New Method for the Generation and Trapping of 1-Azabicyclo[1.1.0]butane. Application to the Synthesis of 1,3-Dinitroazetidine

1-Azabicyclo[1.1.0]butane (1) has been prepared via a two-step, one-pot procedure that involves (i) reaction of a heptane solution of allylamine with N-chlorosuccinimide at 0 °C followed by (ii) codistillation of the product from basic solution along with heptane-octane. Compound 1 thereby obtained was extracted from the distillate by using cold aqueous NaNO₂. Subsequent treatment of the aqueous extract with cold concentrated aqueous HCl afforded N-nitroso-3-nitro-azetidine (4) in 5.5% yield. Oxidation of 4 with 100% HNO3 produced N,3-dinitroazetidine (5, 90%). This reaction sequence constitutes a formal synthesis of 1,3,3-trinitroazetidine (TNAZ), an important energetic material.     

氢化物发生-冷阱捕获-色谱分离-原子吸收法测定天然水中砷的形态

研究建立了氢化物发生－冷阱捕获－色谱分离－原子吸收方法测定天然水中四种主要砷形态。测试系统自行组装，色谱住填料采用ChromosorbGAW－DMCS（粒径0．3～0．45mm），其上涂布3％OV－101。方法的检出限以砷计分别为：As（V）0．51ng，As（Ⅲ）0．43ng，MMA0．38ng，DMA067ng；12ng砷标准偏差As（Ⅴ）4．21％，As（Ⅲ）3．56％，MMA3．23％，DMA5．46％。在0～50ng砷量范围标准曲线线性关系良好。该法适用性广，已用于湖水、河水、海水和地下水等不同水样神形态测定，加标回收率93．5％～104．9％。给出了上述水样四种砷形态的分析结果。     

Trapping silicon surface-based radicals

The spontaneous one-electron reduction of diazonium salts on hydride-terminated porous silicon (pSi) and flat silicon produces surface radicals that can be trapped chemically. These silicon radicals react with reagents such as alkyl/arylselenoethers, alkenes, alkynes, and alkylbromide groups to generate covalently bound functionalities in a manner analogous to the chemistry of molecular-based silicon radical species, prepared via different methods. When pSi is exposed to an acetonitrile solution of any of the three diazonium salts examined in this study, aryl groups from the diazonium precursor become covalently bound and significant oxidation is noted; if, however, a reactive trapping agent is added, such as an alkyl/arylselenoether or a carbon-carbon unsaturated bond, no aryl group attachment is observed and oxidation is circumvented due to the efficiency of the trapping chemistry. The reactions proceed rapidly, in less than 3 h to maximum coverage, at room temperature. The diazonium salt-initiated radical reaction with alpha,omega-alkenes and alkynes tolerates various functional groups including aryl, diene, diyne, carboxylic acid, and hydroxyl, reacting exclusively via the carbon-carbon unsaturated bond; alpha,omega-bromoalkenes are not, however, compatible with this chemistry. A silicon-based molecule, tris(trimethylsilyl)silane, in the presence of a diazonium salt initiator and a primary alkyne does not lead to the hydrosilylation product but to tris(trimethylsilyl)silylbromide and the hydrogenated arene, derived from the diazonium. The difference in reactivity between the molecule and the surface is due to the fact that the silicon surface is a source of electrons to reduce the diazonium salts to aryl radicals, whereas a heterolytic pathway is followed in the molecular silane case.